Solid-state imaging apparatus employing independently variable odd and even lines of photodiodes

ABSTRACT

A solid-state imaging apparatus capable of changing a vertical resolution (MTF) without damaging the dynamic resolution. A CCD drive circuit 6 for driving a CCD image sensor 2 of an imaging section 3 is controlled by a control section 7 to independently vary effective charge storage periods of respective photoelectric conversion of the CCD image sensor 2 with respect to photoelectric conversion of odd columns and photoelectric conversion elements of even columns and to add and mix, every field, image pick-up charges obtained by respective adjacent photoelectric conversion elements of odd and even columns to read them out. A CCD drive circuit 6 for driving a CCD image sensor 2 of an imaging section 3 may also be controlled by a control section 7 to carry out control of the electronic shutter function of the CCD image sensor 2, and to control the effective charge storage periods of respective photoelectric conversion elements in a manner caused to interlock with the electronic shutter function.

This is a continuation of application Ser. No. 08/029,070 filed Mar. 10,1993, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a solid-state imaging or image pickupapparatus adapted to pick up an image of an object by a solid-stateimage sensor in which photoelectric conversion elements are arranged ina matrix form, which is applied to a television camera apparatus of thestandard television system, e.g., the NTSC (National Television SystemCommittee) system, PAL system etc, where an interlaced scanning iscarried out.

Such standard television systems such as the NTSC system, etc., useinterlaced scanning in which scanning lines of odd fields and scanninglines of even fields are alternately positioned.

2. Description of the Prior Art

In a solid-state imaging apparatus using a solid-state image sensor suchas a CCD (Charge Coupled Device) in which photoelectric conversionelements are arranged in a matrix form, approaches have been employed toallow the sensor to be operative in an operational mode called a fieldreadout mode or an operational mode called a frame readout mode, both ofwhich produce an image pickup output of the interlaced scanning type.

For example, in an interline transfer type CCD image sensor, inoperation in the field readout mode, as shown in FIG. 6 of theaccompanying drawings, image pickup charges A_(i) from photoelectricconversion elements of odd columns and image pickup charges B_(i) fromphotoelectric conversion elements of even columns (which arerespectively adjacent to each other) are transferred to verticaltransfer registers by using readout pulses every vertical blankingperiod. Charges from vertically adjacent pairs of photoelectricconversion elements (odd and even) are added together, with the pairingbeing alternated each field (so that a given charge is added to thecharge from above in one field and to the charge below the next field)to line-sequentially read out image pickup charges (A_(i) +B_(i)) then(B_(i) +A_(i+1)) in successive fields. The charges are transferredthrough a horizontal transfer register from the vertical transferregisters during an image period to thereby obtain an image pickupoutput corresponding to the interlaced scanning.

In the case of the operation in the frame readout mode, an approach isemployed as shown in FIG. 7 to transfer, by using readout pulses everyvertical blanking period, image pickup charges A_(i) from photoelectricconversion elements of odd columns and image pickup charges B_(i) fromphotoelectric conversion elements of even columns to the verticaltransfer registers in alternate intervals. Then one after another everyfield those image pickup charges A_(i), B_(i) of respective fields areline-sequentially read out through the horizontal transfer register fromthe vertical transfer registers during an image period to thereby obtainan image pickup output corresponding to the interlaced scanning.

In addition, it has also been proposed to provide an electronic shutterfunction for such image sensors in which, in the above-mentioned fieldreadout mode, control pulses are applied to sweep away image pickupcharges obtained by respective photoelectric conversion elements intothe overflow drain, thereby permitting effective charge storage periods,and thus the effective shutter speed, to be variable.

However, the above techniques have certain disadvantages. In the fieldreadout mode, the addition and mixing of image pickup charges A_(i) ofodd columns and image pickup charges B_(i) of even columns lowers thevertical resolution (Modulation Transfer Function or MTF).

In the frame readout mode, though, as the image pickup charges A_(i) ofodd columns and image pickup charges B_(i) of even columns adjacentthereto are separately read out, the vertical resolution (MTF) isimproved compared to the field readout mode, but there are problems thatwith moving pictures there results an increased after-image and that thedynamic range becomes approximately one half because of the increasedcharge pickup time. In addition, in the case of the frame readout mode,the flicker caused by the interlaced scanning tends to becomeconspicuous.

OBJECTS AND SUMMARY OF THE INVENTION

In view of problems with conventional solid-state imaging apparatus asdescribed above, it is an object of this invention to provide asolid-state imaging apparatus capable of improving the verticalresolution (MTF) with less reduction of the dynamic resolution.

It is a further object of the invention to provide an imaging system inwhich the effect of an electric shutter function on the visualresolution can be reduced.

To solve the above-described problems, a solid-state imaging apparatusaccording to this invention is characterized by the provision of asolid-state image sensor in which photoelectric conversion elements arearranged in a matrix form; and image sensor drive control means adaptedto carry out a control to independently change effective storage periodsof the respective odd and even photoelectric conversion elements of thesolid-state image sensor to add and mix, every field, image pickupcharges obtained by respective adjacent odd and even photoelectricconversion elements in different proportions.

This may be achieved by providing additional read-out pulses (sensorgate pulses) in between the existing sensor gate pulses for,alternately, first the odd sensor elements then, in the next field, theeven sensor elements. Thus in each field one set of sensor elements ismaking a full contribution of charge in the adding and mixing, while theother is reduced because their effective charges storage time wasreduced by the extra intermediate read-out pulse.

Preferably on application of the additional read-out pulse the chargestored up to that point is transferred at high speed and swept away by ahigh speed horizontal pulse (in the horizontal transfer register of anFIT type CCD).

Where an electronic shutter function is provided the additional read-outsignals may be in timed relation to the shutter signals. This allows themixing ratio of contributions respectively from the odd and evenelements to be varied from the normal 1:1 in order to improve thevirtual resolution, but avoids the shutter signal deleteriouslyaffecting the vertical resolution.

In one embodiment, the image sensor drive control means carries outcontrol to read out image pickup charges obtained by photoelectricconversion elements of odd columns and image pickup charges of evencolumns of a solid-state image sensor of the frame interline transfertype to the vertical transfer registers of the imaging section one afteranother every field during for example the middle of an image period.This may follow, and be in timed relation to, a shutter signal. Then ittransfers, at a high speed, those image pickup charges from the verticaltransfer registers of the imaging section to the vertical transferregisters of the storage section during a vertical blanking period everyfield. Then it line-sequentially transfers, at a high speed, imagepickup charges through the horizontal transfer register section from thevertical transfer registers of the storage section to sweep them out.For production of the image signal, the drive control means adds andmixes image pickup charges obtained by the photoelectric conversionelements of the odd columns and the photoelectric conversion elements ofthe even columns adjacent thereto during a vertical blanking periodevery field and reads out these added and mixed image pickup charges tothe vertical transfer registers of the imaging section. It thentransfers, at a high speed, those image pickup charges to the verticaltransfer registers of the storage section, and line-sequentially readsout image pickup charges through the horizontal transfer registersection from the vertical transfer registers of the storage section.

The adding and mixing of charge from adjacent elements may be effectedbefore or after transfer.

The invention will be further described by way of example in thefollowing description of illustrative embodiments given with referenceto the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the configuration of a solid-stateimaging apparatus according to this invention;

FIGS. 2 and 2A are diagrammatic plan views showing the configuration ofCCD image sensors of the frame interline transfer type used in theabove-mentioned solid-state imaging apparatus;

FIG. 3 is a timing chart showing the operation of the above-mentionedsolid-state imaging apparatus according to a first embodiment of theinvention;

FIG. 4 is a characteristic diagram showing a vertical MTF characteristicof image pickup signals obtained by the above-mentioned imagingapparatus;

FIG. 5 is a timing chart showing operation of the above-mentionedsolid-state imaging apparatus according to a second embodiment of theinvention.

FIG. 6 is a timing chart showing the operation in a field readout mode;

FIG. 7 is a timing chart showing the operation in a frame readout mode;and

FIG. 8 is a timing chart showing operation in a field readout mode witha shutter function.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of a solid-state imaging apparatus according to thisinvention and also according to the prior art will now be described indetail with reference to the attached drawings.

A solid-state imaging apparatus using the invention is constructed asshown in FIG. 1, for example.

The solid-state imaging apparatus shown in FIG. 1 is applied to a colourtelevision camera apparatus adapted to pick up three primary colourimages of an object by a CCD (Charge Coupled Device) image sensor 2 ofan imaging section 3 to which an image pickup light L_(i) is incidentthrough an image pickup optical system 1 to output television signals inconformity with the NTSC (National Television System Committee) system.It comprises a signal processing section 4 supplied with image pickupsignals from the imaging section 3, an encoder 5 supplied with imagepickup signals which are processed by the signal processing section 4, aCCD drive circuit 6 for driving the CCD image sensor 2, and a controlsection 7 for controlling the operations of these various circuitblocks, and the like.

In this solid-state imaging apparatus, the CCD image sensor 2 includedin the imaging section 3 is a so-called frame interline transfer (FIT)type CCD image sensor including, as shown in FIG. 2, an imaging sectionIM in which photoelectric conversion elements S₀, S_(E), such asphotodiodes, corresponding to respective pixels of images of odd fieldsand even fields are respectively arranged in a matrix form on theimaging surface, and a storage section ST to which storage chargesobtained by respective photoelectric conversion elements S of theimaging section IM are transferred through vertical transfer registersIMV_(REG). This CCD image sensor 2 is adapted to be driven by the CCDdrive circuit 6, whereby image pickup charges obtained by thephotoelectric conversion elements S₀, S_(E) arranged in a matrix formare transferred from the vertical transfer registers IMV_(REG) of theimaging section IM to the vertical transfer registers STV_(REG) of thestorage section ST through transfer gates SG every vertical blankingperiod, and are line-sequentially read out by one line through thevertical transfer registers STV_(REG) of the storage section ST and thehorizontal transfer register H_(REG) during an image period.

Where an electronic shutter function is provided the CCD image sensor 2is adapted as shown in FIG. 2A so that a shutter pulse ΦSH may beapplied to the substrate or base of the sensor body from the CCD drivecircuit 6, whereby image pickup images obtained by respectivephotoelectric conversion elements S₀, S_(E) of the imaging section IMare swept away into an overflow drain.

The signal processing section 4, of FIG. 1, forms image pickup signalsto which a signal processing such as a gamma (γ) correction isimplemented with respect to image pickup signals read out from the CCDimage sensor 2 to deliver those processed signals to the encoder 5. Theencoder 5 forms television signals in conformity with the NTSC systemfrom the image pickup signals delivered from the signal processingsection 4 to output them from an output terminal 8.

Turning to the operation of the CCD in more detail, the CCD drivecircuit 6 delivers, to the CCD image sensor 2, on the basis of a timingsignal given by the control section 7, various control pulses including:sensor gate pulses ΦSG₁, ΦSG₂ for transferring (reading out) to thevertical transfer registers IMV_(REG) the image pickup charges obtainedby respective photoelectric conversion elements S₀, S_(E) in the imagingsection IM; a vertical transfer pulse ΦIM for transferring, in avertical direction, signal charges in the vertical transfer registersIMV_(REG) of the imaging section IM; a vertical transfer pulse ΦST fortransferring, in a vertical direction, signal charges in the verticaltransfer registers STV_(REG) of the storage section ST; a transfer pulseΦVH for transferring signal charges from the vertical transfer registersSTV_(REG) of the storage section ST to the horizontal transfer registerH_(REG) ; and a horizontal transfer pulse ΦH for transferring, in ahorizontal direction, signal charges in the horizontal transferregisters H_(REG), as well as the shutter pulses (where provided).

On the basis of a system clock of the solid-state imaging apparatus, thecontrol section 7 delivers a synchronizing signal and a blanking signal,etc. to the encoder 5, and delivers various timing signals to the signalprocessing section 4 and the CCD drive circuit 6. This control section 7is adapted so that the operational mode may be switched between severalmodes by a system controller (not shown). To assist understanding, fieldand frame readout modes and an electronic shutter operation as mentionedabove will be described in more detail, before describing operationmodes according to two embodiments of the invention.

The field readout mode will be described in more detail with referenceto FIG. 6.

In this mode, the CCD drive circuit 6 delivers, at the same time, to theimaging section IM, sensor gate pulses ΦSG₁, ΦSG₂ during the verticalblanking period T_(VBLK) every field to allow the vertical registersIMV_(REG) to transfer image pickup charges A_(i) obtained byphotoelectric conversion elements S₀ of odd columns and image pickupcharges B_(i) obtained by photoelectric conversion elements S_(E) ofeven columns. As mentioned above charges from pairs of adjacent odd andeven elements are combined with the combinations being changed everyfield to thereby read out image pickup charges (A_(i) +B_(i)) then(B_(i) +A_(i+1)) corresponding to the interline scanning in the fieldreadout mode. These charges are transferred to the vertical transferregisters IMV_(REG).

Immediately before the timings of the sensor gate pulses ΦSG₁, ΦSG₂ highspeed vertical transfer pulses ΦIM, ΦST are delivered to the verticaltransfer registers IMV_(REG) of the imaging section IM and the verticaltransfer registers STV_(REG) of the storage section ST to allow thevertical transfer registers STV_(REG) of the storage section ST totransfer, at a high speed, unnecessary charges such as a smearcomponents, etc. in the vertical transfer registers IMV_(REG) of theimaging section IM. By this high speed transfer operation, the verticaltransfer registers IMV_(REG) of the imaging section IM are brought intoan empty state where unnecessary charges are swept out therefrom.

Further, immediately before the timings of the sensor gate pulses ΦSG₁,ΦSG₂, the CCD drive circuit 6 delivers high speed vertical transferpulses ΦIM, ΦST to the vertical transfer registers IMV_(REG) the imagingsection IM and the vertical transfer registers STV_(REG) of the storagesection ST to transfer at a high speed image charges A_(i) +B_(i), B_(i)+A_(i+1) from the vertical transfer registers IMV_(REG) of the imagingsection IM to the vertical transfer registers STV_(REG) of the storagesection ST.

The signal charges A_(i) +B_(i), B_(i) +A_(i+1) which have beentransferred at a high speed to the vertical transfer registers STV_(REG)of the storage section ST are line-sequentially read out through thehorizontal transfer register H_(REG) in a later readout period (imageperiod).

The image pickup signal which has been read out from the solid-stateimage sensor 1 is delivered to the encoder 5 though the signalprocessing section 4, at which it is encoded so that a television signalin conformity with a desired (e.g. NTSC) system is provided. The signalthus obtained is outputted from the output terminal 8.

This mode may also have an electronic shutter operation in which the CCDdrive circuit 6 applies a shutter pulse ΦSH to the substrate or base ofthe CCD image sensor 2 in the middle of an image period as shown inFIGS. 2A and 8. Thus, in the CCD image sensor 2, image pickup chargesobtained by respective photoelectric conversion elements S₀, S_(E) ofthe imaging section IM are swept away into the overflow drain at everyapplication of the shutter pulse ΦSH. As a result, the effective chargestorage period T_(EXP) following the shutter pulse is variablycontrolled by varying the timing of the shutter pulse.

Similarly to the non-shutter operation the CCD drive circuit 6 deliverssensor gate pulses ΦSG₁, ΦSG₂ in the state where the vertical transferregisters IMV_(REG) are caused to be empty (by high speed verticaltransfer pulses ΦIM, ΦST) to thereby allow the vertical transferregisters IMV_(REG) to transfer image pickup charges A_(i), B_(i) (orB₁₊₁) obtained by the photoelectric conversion elements in the imagingsection IM with the combinations of image pickup charges of respectivecorresponding odd and even columns being changed one after another everyfield. These are transferred to the vertical transfer registersSTV_(REG) of the storage section ST, at a high speed and are read outthrough the horizontal transfer register H_(REG) in a later readoutperiod (image period).

Thus, in this mode, it is possible to variably control the effectivecharge storage period T_(EXP) by the electronic shutter function. Theimage pickup signal which has been read out from the solid-state imagesensor 1 is delivered to the encoder 5 through the signal processingsection 4, at which it is encoded so that a television signal inconformity with a desired system is provided. The signal thus obtainedis outputted from the output terminal 8.

The second operational mode is a frame readout mode and this will bedescribed with reference to FIG. 7.

In this second operational mode, the CCD drive circuit 6 delivers, tothe imaging section IM, sensor gate pulses ΦSG₁, ΦSG₂ one after anotherevery field during the vertical blanking period T_(VBLK) to allow thevertical transfer registers IMV_(REG) to receive image pickup chargesA_(i) obtained by photoelectric conversion elements S₀ of odd columnsand image pickup charges B_(i) obtained by photoelectric conversionelements S_(E) of even columns one after another every field. Theseimage pickup charges A_(i), B_(i) corresponding to the interlinescanning in the frame readout mode are then read out.

It is to be noted that, also in this second operational mode,immediately before the timings of the sensor gate pulses ΦSG₁, ΦSG₂,high speed vertical transfer pulses ΦIM, ΦST are respectively deliveredto the vertical transfer registers IMV_(REG) of the imaging section IMand the vertical transfer registers STV_(REG) of the storage section STto transfer, at a high speed, unnecessary charges such as smearcomponents, etc. from the vertical transfer registers IMV_(REG) of theimaging section IM to the vertical transfer registers STV_(REG) of thestorage section ST. By this high speed transfer operation, the verticaltransfer registers IMV_(REG) of the imaging section IM are placed in anempty state where any unnecessary charges are swept out therefrom.

Then, the CCD drive circuit 6 delivers the sensor gate pulses ΦSG₁, ΦSG₂in the state where the vertical transfer registers IMV_(REG) are empty.

That is, immediately before the timings of the sensor gate pulses ΦSG₁,ΦSG₂, the CCD drive circuit 6 delivers high speed vertical transferpulses ΦIM, ΦST to the vertical transfer registers IMV_(REG) of theimaging section IM and the vertical transfer registers STV_(REG) of thestorage section ST to transfer, at a high speed, charges A_(i), B_(i) inthe vertical transfer registers IMV_(REG) of the imaging section IM tothe vertical transfer registers STV_(REG) of the storage section ST.

The signal charges A_(i), B_(i) which have been transferred at a highspeed to the vertical transfer registers STV_(REG) of the storagesection ST are read out through the horizontal transfer register H_(REG)for a later readout period.

An image pickup signal read out from the solid-state image sensor 1 isdelivered to the encoder 5 through the signal processing section 4, atwhich it is encoded so that a television signal in conformity with adesired system is provided. The signal thus obtained is outputted fromthe output terminal 8.

Having described these modes, two modes of operation according to thepresent invention will now be described.

In the first embodiment, as shown in FIG. 3, the CCD drive circuit 6delivers, to the imaging section IM, sensor gate pulses ΦSG₁, ΦSG₂during a vertical blanking period T_(VBLK) every field. These areadapted to cause the vertical transfer registers IMV_(REG) to transferimage pickup charges A_(i) obtained by photoelectric conversion elementsS₀ of odd columns and image pickup charges B_(i) obtained byphotoelectric conversion elements S_(E) of even columns during avertical blanking period T_(VBLK) every field to the vertical transferregister IMV_(REG). As before, signals from pairs of adjacent elementsare combined with the pairing of the image pickup elements beingalternated every field to thereby read out image pickup charges A_(i)+B_(i), and then B_(i) +A_(i+1) corresponding to the interline scanningin the field readout mode.

Also as before, immediately before the timings of sensor gate pulsesΦSG₁, ΦSG₂, that is, every respective vertical blanking periodsT_(VBLK), high speed vertical transfer pulses ΦIM, ΦST are respectivelydelivered to the vertical transfer registers IMV_(REG) of the imagingsection IM and the vertical transfer registers STV_(REG) of the storagesection ST to clear the registers. Thus the sensor gate pulses ΦSG₁,ΦSG₂ are applied in the state where the vertical transfer registersIMV_(REG) are empty.

Similarly, immediately after the timings of the sensor gate pulses ΦSG₁,ΦSG₂, the CCD drive circuit 6 delivers the high speed vertical transferpulses ΦIM, ΦST to the vertical transfer registers IMV_(REG) of theimaging section IM and the vertical transfer register STV_(REG) of thestorage section ST, thus to transfer, at a high speed, charges A_(i)+B_(i), B_(i) +A_(i+1) in the vertical transfer registers IMV_(REG) ofthe imaging section IM to the vertical transfer registers STV_(REG) ofthe storage section ST.

In this embodiment, and as shown in FIG. 3, during high speed transferperiod by the vertical transfer registers STV_(REG), the horizontaltransfer pulse ΦH is also caused to be a high speed pulse to therebysweep out unnecessary charges by high speed transfer through thehorizontal transfer register H_(REG). Thus, image pickup charges A_(i),of photoelectric conversion elements S₀ of odd columns and image pickupcharges B_(i), of even columns read out to the vertical transferregister IMV_(REG) of the imaging section IM by delivering sensor gatepulses ΦSG₁, ΦSG₂ to the imaging section IM one after another everyfield during image periods of respective fields are swept out asunnecessary charges. Accordingly, a large quantity of unnecessarycharges will be produced. However, by the above-mentioned high speedtransfer, it is possible to sweep out such a large quantity ofunnecessary charges through the horizontal transfer register H_(REG).

Namely, the horizontal transfer register H_(REG) can sweep out a largequantity of unnecessary charges by increasing the number of transfertimes by the high speed transfer even if a quantity of chargestransferred every transfer is small.

Also in this embodiment the sensor gate pulses ΦSG₁, ΦSG₂ delivered tothe imaging section IM are adapted as shown in FIG. 3 to carry out adummy readout alternately of image pickup charges A_(i) obtained byphotoelectric conversion elements S₀ of odd columns in one field andthen image pickup charges B_(i) obtained by photoelectric conversionelements S_(E) of even columns in the next field. Thus for each of theodd elements and even elements in every alternate period between thesuccessive sensor gate pulses an additional sensor gate pulses isapplied. The extra pulses alternate between the odd and even elements sothat in one field the odd elements have the extra pulse and in the nextfield the even elements have it. As the signals from odd and evenelements are then paired these extra pulses make it possible to changethe additive mixing ratio of image pickup charges A_(i) +B_(i), B_(i)+A_(i+1) every field from the additive mixing ratio of 1:1 for anordinary field readout mode. With the arrangement shown in FIG. 3 theabove-mentioned additive mixing ratio is, 1:2, as for the element towhich the extra pulse is supplied, half the charge accumulated(A_(i),B_(i)) is discarded by using the above-mentioned high speed pulseand only half is added to the charge (B_(i),A_(i)) from the otherelement which has been accumulating for twice as long.

The signals are line-sequentially read out through the horizontaltransfer register H_(REG) from the vertical transfer registers STV_(REG)of the storage section ST during an image period to thereby obtain animage pickup output corresponding to the interlaced scanning in thefield readout mode. Then, an image pickup signal read out from thesolid-state image sensor 1 is delivered to the encoder 5 through thesignal processing section 4, at which it is encoded so that a televisionsignal in conformity with the NTSC system is provided. The signal thusobtained is outputted from the output terminal 8.

By varying the additive mixing ratio between image pickup charges A_(i)obtained by photoelectric conversion elements S₀ of odd columns andimage pickup charges B_(i) obtained by photoelectric conversion elementsS_(E) of even columns in this way, it is possible, as shown in FIG. 4,to obtain an intermediate vertical resolution (MTF) between a verticalresolution in the first operational mode, i.e., an ordinary fieldreadout mode and that in the second operational mode, i.e., the framereadout mode. Assuming now that the above-mentioned additive mixingratio is, for example, 1:2, an image pickup output corresponding to theinterlaced scanning in the field readout mode is provided, therebymaking it possible to improve a vertical resolution as compared to theordinary field readout mode. In addition, the dynamic range and thesensitivity can be maintained at 75%, thus making it possible to improvethe dynamic range and the sensitivity to a greater degree as compared tothe frame readout mode.

As is clear from the foregoing description, in the solid-state imagingapparatus according to this embodiment of the invention, image pickupcharges alternately obtained by photoelectric conversion elements of oddcolumns and image pickup charges obtained by photoelectric conversionelements of even columns of a solid-state image sensor of the frameinterline transfer type are read-out one after another every field inthe middle of an image period, thereby making it possible toindependently vary effective charge storage periods of respectivephotoelectric conversion elements in the pairs which are combined. Thisallows variation of vertical resolution in dependency upon the additivemixing ratio. During a vertical blanking period every field, imagepickup charges read out to the vertical transfer registers of theimaging section one after another every field in the middle of the imageperiod are transferred, at a high speed, from the vertical transferregisters of the imaging section to the vertical transfer registers ofthe storage section, and are further line-sequentially transferred at ahigh speed through the horizontal transfer register from the verticaltransfer registers of the storage section. Image pickup charges thustransferred are swept out as unnecessary charges. As stated above, thehorizontal transfer register can sweep out a large quantity ofunnecessary charges during a vertical blanking period every field byincreasing the number of transfer times by the high speed transfer evenif a quantity of charges transferred every transfer is small. This makesit possible to provide an image pickup output in which the degree oflowering of the vertical resolution (MTF) is less than in the case ofthe field readout mode, an after-image is less than that in the case ofthe frame readout, and the dynamic range is wide.

Now a second embodiment of the solid-state imaging apparatus accordingto this invention will be described with reference to FIG. 5.

In this embodiment, the CCD drive circuit 6 applies a shutter pulse ΦSHto the substrate of the CCD image sensor 2 at a variable time pointduring an image period. Thus, in the CCD image sensor 2, image pickupcharges obtained by respective photoelectric conversion elements S₀,S_(E) of the imaging section IM are swept away into the overflow drainon every shutter pulse ΦSH. As a result, the effective charge storageperiod T_(EXP) is variably controlled.

Then, the CCD drive circuit 6 delivers, to the imaging section IM,sensor gate pulses ΦSG₁, ΦSG₂ as in the first embodiment during imageperiod of respective fields in a manner to interleave with the shutterpulse ΦSH during image periods of respective fields. The sensor gatepulses ΦSG₁, ΦSG₂ are delivered during the vertical blanking periodT_(VBLK) every field to allow the vertical transfer registers IMV_(REG)to transfer image pickup charges A_(i) obtained by photoelectricconversion elements S₀ of odd columns and image pickup charges B_(i)obtained by photoelectric conversion elements S_(E) of even columns inpairs, with the pairings of the image pickup charges of respectivecorresponding odd and even columns being alternated every field, tothereby read out, to the vertical transfer registers IMV_(REG), imagepickup charges A_(i) +B_(i) then B_(i) +A_(i+1) corresponding to theinterline scanning in the field readout mode.

As explained below, in this embodiment the sensor gate pulses areadapted to allow the additive mixing ratio of image pickup charges A_(i)+B_(i) corresponding to the interline scanning to be fixed.

Also, as before, immediately before the timings of sensor gate pulsesΦSG₁, ΦSG₂, that is, in every respective vertical blanking periodsT_(VBLK), high speed vertical transfer pulses ΦIM, ΦST are respectivelydelivered to the vertical transfer registers IMV_(REG) of the imagingsection IM and the vertical transfer registers STV_(REG) of the storagesection ST to allow the vertical transfer registers STV_(REG) of thestorage section ST to transfer, at a high speed, unnecessary chargessuch as smear components, etc. from the vertical transfer register ofthe imaging section IM.

Further, immediately after the timings of the sensor gate pulses ΦSG₁,ΦSG₂, the CCD drive circuit 6 delivers high speed vertical transferpulses ΦIM, ΦST to the vertical transfer registers IMV_(REG) of theimaging section IM and the vertical transfer register STV_(REG) of thestorage section ST, thus to allow the vertical transfer registersSTV_(REG) of the storage section ST to transfer, at a high speed, imagecharges A_(i) +B_(i) from the vertical transfer registers IMV_(REG) ofthe imaging section IM.

According to the invention, while the effective charge storage periodT_(EXP) is variable by the control of the electronic shutter function,during image periods of respective fields, sensor gate pulses ΦSG₁, ΦSG₂are delivered to the imaging section IM one after another every fieldwhich carry out a dummy readout of image pickup charges A_(i) obtainedby photoelectric conversion elements S₀ of odd columns and image pickupcharges B_(i) obtained by photoelectric conversion elements S_(E) ofeven columns one after another every field. This consists of theadditional application in alternate periods between successive sensorgate signals, both in ΦSG₁, ΦSG₂, of a variably-timed extra sensor gatepulse as shown in FIG. 5. The extra pulse alternates between odd andeven elements as before, thereby making it possible to change theadditive mixing ratio of image pickup charges A_(i) +B_(i) every fieldfrom the additive mixing ratio of 1:1 in an ordinary field readout mode.The above-mentioned additive mixing ratio may be changed, for example,to 1:2.

By varying the additive mixing ratio between image pickup charges A_(i)obtained by photoelectric conversion elements S₀ of odd columns andimage pickup charges B_(i) obtained by photoelectric conversion elementsS_(E) of even columns in this way, it is possible to obtain, as shown inFIG. 4, an intermediate vertical resolution (MTF) between a verticalresolution in the first operational mode, i.e., an ordinary fieldreadout mode and that in the second operational mode, i.e., the framereadout mode.

Further, the dynamic range and the sensitivity can be maintained at 75%,thus making it possible to improve the dynamic range and the sensitivityto a greater degree as compared to the second operational mode, i.e.,the frame readout mode. In addition, in the case where the effectivecharge storage period T_(EXP) is caused to be variable by the control ofthe electronic shutter function, sensor gate pulses ΦSG₁, ΦSG₂ deliveredone after another every field to the imaging section IM during imageperiods of respective fields are caused to interleave with the shutterpulse ΦSH, resulting in no possibility that the vertical resolution(MTF) is changed by the above-mentioned shutter function because theadditive mixing ratio is effectively fixed irrespective of the controlof the electronic shutter function.

As is clear from the foregoing description, in the solid-state imagingapparatus according to this embodiment of the invention, it is possibleto provide an image pickup output in which the degree of lowering of thevertical resolution (MTF) is less than that in the case of the fieldreadout mode, an after-image is less than that in the case of the framereadout mode, and the dynamic range is wide. Further, by using the imagesensor drive control means the electronic shutter function is controlledto carry out an imaging operation in which the effective charge storageperiod is caused to be variable by the control of the electronic shutterfunction without change of the vertical resolution (MTF).

Accordingly, in accordance with this invention, there can be provided asolid-state imaging apparatus in which the vertical resolution can bevaried without damaging the dynamic resolution by a solid-state imagesensor having an electronic shutter function.

We claim:
 1. A solid-state imaging apparatus comprising:a solid-stateimage sensor in which a plurality of photoelectric conversion elementsfor storing charges in response to illumination by image light arearranged on a substrate in a matrix form having odd and even lines; andimage sensor drive control means for applying first read-out pulses tothe photoelectric conversion elements for each field so as to formeffective charge storage periods and for applying second read-out pulsesarranged between said first read out pulses so as to independently varythe effective charge storage periods of each of said odd and even linesof the photoelectric conversion elements, said second read-out pulsesbeing applied in each field alternately to the odd and even lines of thephotoelectric conversion elements; and wherein said image sensor drivecontrol means applying an electronic shutter signal to said substrate toaffect simultaneously both said odd and even lines of said photoelectricconversion elements of said image sensor to sweep out image pickupcharges into an overflow drain and to allow said effective chargestorage periods of said odd and even lines of photoelectric conversionelements to be independently varied by applying said second read-outpulses between said first read-out pulses in timed relation to theelectronic shutter signal; and wherein said image sensor drive controlmeans applying said first and second read-out pulses to the plurality ofphotoelectric conversion elements to add for every field image pick-upcharges obtained from pairs of photoelectric conversion elements fromeach of an adjacent odd and even line, in which a pairing ofphotoelectric conversion elements whose charges are added is varied byadding in a first field the charge from an element in a first line tothe charge from the corresponding element in the preceding adjacentline, and in a second field by adding the charge from the element in thefirst line to the charge from the corresponding element in the nextsucceeding line.
 2. A solid-state imaging apparatus according to claim1, wherein the second read-out pulses follow the electronic shuttersignal.
 3. A solid-state imaging apparatus according to claim 1, whereinthe image sensor drive control means generates the second read-outpulses at a timing which maintains constant a mixing ratio of signalsfrom the elements in the pairs of the plurality of photoelectricconversion elements.